Question: Luis just found beautiful yarn for 20 percent off at his favorite yarn store. He can make 1 scarf from $\frac{2}{5}$ of a ball of yarn. If Luis buys 10 balls of yarn, how many scarves can he make?
Solution: We can divide the balls of yarn (10) by the yarn needed per scarf ( $\frac{2}{5}$ of a ball) to find out how many scarves Luis can make. $ \dfrac{{10 \text{ balls of yarn}}} {{\dfrac{2}{5} \text{ ball per scarf}}} = {\text{ number of scarves}} $ Dividing by a fraction is the same as multiplying by the reciprocal. The reciprocal of ${\dfrac{2}{5} \text{ ball per scarf}}$ is ${\dfrac{5}{2} \text{ scarves per ball}}$ $ {10\text{ balls of yarn}} \times {\dfrac{5}{2} \text{ scarves per ball}} = {\text{ number of scarves}} $ ${\dfrac{50}{2}\text{ scarves}} = 25\text{ scarves}$ Luis can make 25 scarves.